Knitted electrodes in the garment are made of conductive yarn, which conductive yarn is knitted together with other basic yarns such as Nylon, bare spandex, covered spandex and/or other types of yarn.
The positioning of an electrode against a monitored living body is of critical importance for obtaining proper ECG signals, especially when the monitored living body is in motion. Moreover, the repeatability of the electrodes location on the body is of critical importance for comparing ECG signals in separate measurement sessions.
When designing a knitted ECG garment, there is a need to ensure that the electrodes are repeatably positioned at the same respective pre-configured positions with respect to the monitored living body, for a given garment size designated to be worn by a variety of people. Usually, people of the same size have different body structure, weight and height, which may affect the respective position of the electrodes on their body, though the garment is of the same size.
Being knitted in a fabric, the electrodes gain a natural stretch, which stretch may affect the quality by introducing artifacts and damage the repeatability of the recorded ECG signals. Furthermore, garment being knitted, and thereby stretchable, may cause the electrodes to move with respect to the adjacent skin of the wearer, which may further affect the quality by introducing artifacts and damage the repeatability of the recorded signals. These damaging artifacts may occur because of changes in the electrode electrical characteristics, and may cause unnecessary noises in the system during breathing and bodily motions, wherein the spatial positioning of an electrode, with respect to the monitored organ, may change.
There is a need to stabilize the bodily position of the sensing knitted electrodes with respect to the skin of the wearer, in order to obtain a stable signal through the skin, the skin having a high impedance. In order to achieve a stable biological signal (such as ECG) reading, one needs to establish a stable interface between the electrodes and the skin of the wearer. The biological signal source needs to face stable resistance values that have only small variations as a result of breathing or shifting in the electrode position relative to the biological signal source.
In electric terms, the voltage sensed by the electrode can be represented by: E=I×Z. When the electrical impedance Z is substantially constant, as desired, the voltage E measured by the electrode depends only on changes of the current I and that is exactly what we want to measure. That is, the electrode size or re-positioning should not affect the measurement of voltage E. we want to sense only the signal changes that result from the biological changes such as the heart activity, when measuring ECG.
By the retention of physical dimensions, that is area size and impedance, of the knitted electrode, one can obtain a signal that is not affected by changes damaging artifact but a signal representing only the physiological changes of the body.
There is therefore a need and it would be advantageous to have methods for knitting a garment such that the elasticity of one or more selected regions is stabilized, for example by rigidifying the selected regions and thereby maintain the original dimensions of these regions. Furthermore, there is a need for a stable and repeatable positioning of electrodes at respective pre-configured bodily location, which positioning is of extreme importance to obtain good ECG signals, facilitating clinical level ECG, while the monitored person is either in rest or is moving, jumping or walking.
It should be noted that the term “ECG signals”, as used herein, refers to any physiological signal of the monitored living being that can be sensed directly or indirectly by an electrode, including signals for ECG analysis.
The terms “underwear” or “garment”, as used herein with conjunction with wearable clothing items, refers to seamless wearable clothing items that preferably, can be tightly worn adjacently to the body of a monitored living being, typically adjacently to the skin, including undershirts, sport shirts, brassiere, underpants, special hospital shirts, socks and the like. Typically, the terms “underwear” or “garment” refer to a clothing item that is worn adjacently to the external surface of the user's body, under external clothing or as the only clothing, in such a way that the fact that there are sensors embedded therein, is not seen by any other person in regular daily behavior. An underwear item may also include a clothing item that is not underwear per se, but still is in direct and preferably tight contact with the skin, such as a T-shirt, sleeveless or sleeved shirts, sport-bra, tights, dancing-wear, and pants. The sensors, in such a case, can be embedded in such a way that they remain unseen by external people to comply with the “seamless” requirement.
The phrase “clinical level ECG”, as used herein with conjunction with ECG measurements, refers to the professionally acceptable number of leads, sensitivity and specificity needed for a definite conclusion by most cardiology physicians to suspect a risky cardiac problem (for example, arrhythmia, myocardial ischemia, heart failure) that require immediate further investigation or intervention. Currently, it is at least a 12-leads ECG and preferably 15-lead ECG, coupled with a motion/posture compensation element, and a real-time processor with adequate algorithms.
The phrase “base-yarn”, as used herein, refers to the yarn from which the fabric of the garment is knitted. The fabric is typically knitted with Nylon, bare Spandex and covered spandex. In another example embodiment, the fabric is typically knitted with a base-yarn such as Nylon and covered spandex. It should be noted that such a garment can be knitted with any type of base-yarn, including Nylon yarn textured or flat, selected types of Nylons, Polyester, Polypropylene, Acetate, manmade fibers, natural yarns like cotton, bamboo, wool, and blends of the mentioned raw materials. Selection of yarn is also based on fabric weight, body size for men and women, fabric weight and design requirements.